It’s similar to faking stupidity. She laughs after realizing that she was totally misunderstood and her meaning is twisted into some foolish statement.
For example, if things are really going well between you two and she asks, “Do you want to go into my bedroom?” Instead of getting all excited you can tell her as if you don’t get it, “No. I prefer to stay here with you.”
When the two of you decide to go out and she says, “I can’t pick a date”, you can reply, “Who do you want to bring as a date?”
Don’t restrict your misinterpretation to only the words she says. You can virtually twist any piece of information. Just make sure you don’t sound truly stupid. For example, nowadays you see numbers printed on t-shirts. If next time she wears one with a pretty big number like “162”, point at it and ask her, “How did they know you’re 162 pounds?”